In the past, conventional blinds for windows have typically been either venetian style blinds with transverse strips, or so called vertical blinds. These blinds could have a mechanism whereby the strips could be rotated between closed and open positions. However in the open position, in which light is transmitted into the room, there was also a loss of privacy. In the closed position, the light was obscured.
Other blinds are known which simply consist of a panel of thick flexible material, wound onto a roller in a head rail. The material can be pulled down for privacy, and to obscure the light, or raised, to, allow passage of light, but with loss of privacy.
Recent developments in blind design have found that consumers are interested in obtaining blinds with a greater variety of light and shade effects, but which none the less provide for privacy.
For this purpose, a continuous sheet of blind material may be provided, which hangs down double, over the window opening, and forms a loop. The sheet is preferably somewhat translucent and is stored on a roller in the head rail. The free end of the sheet is fixed up in the head rail, and the other end of the sheet is attached to the roller in the head rail. This material is light permeable, but provides privacy. For example the material may have alternating bars or strips of more and less translucent material. When hanging in a loop the material will allow more light through the more translucent lighter strips and less through the less translucent darker strips. By adjusting the loop it is possible to allow more light into the space. But by slightly readjusting the loop so as to bring the darker strips into registration, it is possible to reduce the light in the space.
The blind may incorporate a bottom rail which is weighted to keep the loop hanging down. A free running guide roller may be incorporated in the bottom rail. The loop runs freely, in the bottom rail, around the guide roller. In this way the material can be adjusted, or can be retracted right up into the head rail.
In another embodiment a second blind panel is stored in the head rail and is formed of opaque material. When complete light exclusion is required this second panel can be lowered. In this embodiment both blind panels are stored in the same head rail, on separate rollers.
The design of a blind header rail providing two rollers, for handling two such panels, and which may provide for relative movement between one portion of the first panel and another portion, and also the provision of the second roller for the second panel, presents numerous problems. In the first place the head rail must be compact and aesthetically pleasing. Desirably the blind head rail shall occupy no more space, or only slightly more space at the top of the window opening than previously known blinds. The operation of the separate blind panels must be simple and capable of being operated by either manual controls, or in the case of more complex designs by means of power controls, and even remotely operated power controls.
The rollers will preferably be arranged as upper and lower rollers. Each roller would carry a blind panel. The upper blind, on the upper roller, will be guided to pass around the lower roller, and separate from the lower blind, on the lower roller. Where the lower blind is a double panel, with a weighted bottom rail, the lower blind passes around a free running guide roller within the bottom rail. When the lower blind is retracted up, the material continues to roll freely around the guide roller in the bottom rail.
In addition, it is also desirable to provide mechanism for the upper roller and mechanism for the lower roller in the blind head rail by which either or both of lower and upper panels can be raised up out of the window opening, so as to leave the window opening clear and free of the blind all together.
The blind controls are usually chains or cords, hanging down from the head rail, and controlling the rollers. One of the problems experienced with such cords is that some space must be allowed for the cord loops to hang beside one edge of the blind panels. This space along one vertical edge of the blind panels, then allows some light in, and the blind fails to obscure all light.
Another problem is that when an operator manipulates the cords, the edges of the panels gradually become damaged. The appearance, and life, of the blind is therefor impaired.
Another problem occurs from possible friction within the head rail. Since there are two blind panels, and two blind panel rollers, in the head rail, it is desirable to lead one blind panel in a path which minimizes contact with the other blind panel. Any such contact between the two blind panels, may cause friction between them, when either panel is adjusted. Such friction in some cases may result in some degree of damage to one or other of the panels. In some cases a certain degree of friction may be inevitable, and may be acceptable in lower cost blinds, or may be reduced by the use of materials which generate less friction.